Semiconductor electron detector

ABSTRACT

An electron detector particularly adapted to sense low energy radiation, includes a semiconductor crystal having a face directly exposed to the electrons to be detected and provided over its area with an electrode constituted by a light impervious, but electron pervious layer. The crystal further has another face, also carrying an electrode. Within the crystal there is an active zone which, generated by a voltage applied by the electrodes in a blocking direction, extends through the entire crystal between the electrodes.

United States Patent lnventors Peter Glasow Numberg; Prabuddha Banerjee, Karlsruhe, both of, Germany Appl. No. 817,672 Filed Apr. 21, 1969 Patented June 22, 1971 Assignee Siemens Aktiengesellschaft Berlin and Munich, Germany Priority MaySO, 1968 Switzerland 8647/68 SEMICONDUCTOR ELECTRON DETECTOR 4 Claims, 1 Drawing Fig.

US. Cl 250/83 R G0it 1/24 Field of Search 250/83, 83.3, 495

[56] References Cited UNITED STATES PATENTS 2,694,112 [1/1954 McKay 250/833 X 3,293,435 12/1966 Huth 250/833 Primary Examiner-Archie R. Borchett Assistant Examiner-Davis L. Willis Attorney-Edwin E. Greigg ABSTRACT: An electron detector particularly adapted to sense low energy radiation, includes a semiconductor crystal having a face directly exposed to the electrons to be detected and provided over its area with an electrode constituted by a light impervious, but electron pervious layer. The crystal further has another face, also carrying an electrode. Within the crystal there is an active zone which, generated by a voltage applied by the electrodes in a blocking direction, extends through the entire crystal between the electrodes.

SEMICONDUCTOR ELECTRON DETECTOR BACKGROUND OF THE INVENTION Semiconductor devices for detecting low energy electrons (E l kev.) are known in the art. They are in general semiconductor crystals (diodes) having an extremely thin window layer at one face.The material of the semiconductor is usually silicon, while the window layer is made by the vapor deposition of a thin gold layer or by the diffusion of foreign atoms (such as P, B, or Li). The semiconductor detector is mounted in a holder mechanism in such a manner that the window layer is directly exposed to the electrons to be detected. A structure of this type has the disadvantage that the front layer of the semiconductor may be accidentally contacted by mechanical parts and/or may remain freely accessible by the humidity of air. Furthermore, such detectors, whether boundary layer counters or diffused semiconductors, are extremely light sensitive so that measures have to be taken for darkening the environment. In the latter case, however, continuous care has to be taken to avoid an absorption by the darkened environment of a large part of the particles to be detected.

OBJECT AND SUMMARY OF THE INVENTION In order to obviate the aforenoted disadvantages, according to the invention, to a semiconductor electron detector of the type comprising a silicon crystal having an extremely thin, vapor-deposited window layer at one face, a blocking layer at another, opposite face and an internally disposed active zone, there is applied an electric voltage, to said layers as electrodes in the blocking direction causing the active zone to extend over the entire semiconductor detector. Further, the window layer is formed of a light impervious, but electron pervious, metallic, preferably aluminum, layer which is directly exposed to the electrons to be detected. The entire semiconductor detector, with the exception of the face coated with aluminum, is embedded in an insulating material.

The invention will be better understood and further objects, as well as advantages, will become apparent from the ensuing detailed specification of a preferred, although exemplary, embodiment of the invention taken in conjunction with the sole figure schematically showing the semiconductor electron detector device in side elevational section.

DESCRIPTION OF THE EMBODIMENT Turning now to the figure, there is shown a semiconductor detector 1 which has an internally disposed active layer. Ionizing particles or energy elements which impinge on the semiconductor detector 1 from above in the direction of the arrows, generate dipoles along their path inside the semiconductor detector. Those dipoles which are generated inside the active layer contribute to the signal current of the detector 1. The other dipoles are lost by recombination. Thus, in known semiconductor detectors, in case of low energy electrons, this active layer should be as close to the face 2 of the semiconductor detector 1 as possible, in order to pick up the largest possible number of generated dipoles. Consequently, only very shallowly diffused PN junctions or counters having a surface blocking layer (such as gold layer 3 provided on surface 2 in the illustrated'embodiment) may be considered. By applying in the blocking direction of the semiconductor detector 1, a voltage U to the terminals 4 (connected to the electrode constituted by the gold layer 3) and 5 (connected to the electrode constituted by the metal layer 6 on face 7), the active zone may be inwardly extended. By taking appropriate measure (using thin, highly ohmic silicon wafers such as, for example, those finding application in de/dx-counters the active zone may be extended as far as the surface 7. In such case the surface 7 is adapted to detect slow electrons to the same extent as the surface 2.

The surface 7, which in detectors known heretofore formed the back side thereof, is insensitive to a great extent to accidental mechanical contacts. In addition, in order to provide a nonblocking contacting electrode, the semiconductor detector is provided with a vapor-deposited aluminum window layer 6. Since aluminum is a good light absorber, in case of careful vapor deposition, this side of the semiconductor detector 1 will be entirely light impervious. The approximately 2,000 A. thick aluminum layer 6 is, however, pervious to electrons. The entire semiconductor detector 1 is peripherally embedded or framed in a ring 8 of insulating material which, in turn, is held in a metal housing 9. The sensitive surface 2 is thus disposed inside the metallic housing 9 and is protected against any accidental mechanical contact. From the gold blocking layer 3 there extends a conductor 10 for carrying the signal .current generated by the electron beam.

A semiconductor detector of the aforedescribed type is extremely robust, light impervious and may be advantageously used for detecting low energy electrons (E l00 kev.).

What we claim is:

1. In an electron detector of the type including a semiconductor having two opposite outer faces each provided with an electrode, the improvement comprising,

A. a light impervious, but electron pervious metal layer forming one of said electrodes and exposed directly to electrons to be detected,

B. a blocking layer forming the other of said electrodes,

C. an active zone extending entirely through said semiconductor from said blocking ayer to said light impervious, but electron pervious layer and D. means for applying a voltage through said electrodes to said semiconductor in theblocking direction to generate said active zone.

2. An improvement as defined in claim 1, wherein said semiconductor detector is fonned of a silicon crystal coated on one face with a gold layer constituting said blocking layer.

3. An improvement as defined in claim 1, wherein said light impervious, but electron pervious metal layer is formed of aluminum.

4. An improvement as defined in claim 1, wherein said semiconductor detector is framed by an insulating material held in a housing in such a manner that said blocking layer is directed inwardly, and said light impervious, but electron pervious metal layer is directed outwardly of said housing. 

2. An improvement as defined in claim 1, wherein said semiconductor detector is formed of a silicon crystal coated on one face with a gold layer constituting said blocking layer.
 3. An improvement as defined in claim 1, wherein said light impervious, but electron pervious metal layer is formed of aluminum.
 4. An improvement as defined in claim 1, wherein said semiconductor detector is framed by an insulating material held in a housing in such a manner that said blocking layer is directed inwardly, and said light impervious, but electron pervious metal layer is directed outwardly of said housing. 